The present invention relates to a new and improved construction of a friction spinning drum of the type comprising a hollow perforated drum designed for substantially radial throughflow of air.
Such friction spinning drums are used in known friction spinning processes or methods in which usually two cylindrical drums arranged adjacent each other rotate in the same direction, at least one of the two drums being a perforated drum as above described.
The purpose of such perforated drum is to take up fibers fed thereto in known manner by means of an airstream and to twist them into a yarn in the region of convergence of the two friction spinning drums. The yarn is withdrawn in a direction substantially at right angles to the direction of rotation of the friction spinning drums.
The airstream required to feed the fibers is drawn through the holes or perforations of the perforated drum by means of a suction nozzle provided in the interior of such perforated drum.
It therefore should be manifest that, on the one hand, the holes or perforations of the perforated drum must have a diameter which substantially prevents too many fibers being taken up or engaged by the holes or perforations during deposition on the perforated drum and then being either sucked away and hence lost, or at least being cut on the edge of the mouth of the suction nozzle and thereby undesirably shortened.
On the other hand, the energy consumption of such equipment must be held as low as possible, the airflow representing a significant proportion of the energy consumption. From this standpoint, it is desirable to design the holes or perforations of the perforated drum with the largest possible diameter to present the lowest possible resistance to the required throughflow quantity of air per unit time.
These two requirements placed on the diameter of the holes or perforations are diametrically opposed to each other.
In normal practice, and from patent publications, it is known that these holes or perforations generally have a diameter between 0.5 and 0.8 mm.
On the other hand, the perforated drums must have inherent stiffness or rigidity in order to avoid deformation during use, thereby requiring a minimum wall thickness of at least 1.5 mm in such perforated drums when made of brass with, for example, a drum diameter of 50 mm.
It is, however, clear that boring or otherwise fabricating such small holes in a material of 1.5 mm thickness or greater cannot be carried out without problems. Thus such operation is therefore expensive, particularly when the number of holes or perforations per perforated drum is of the order of several tens of thousands.
When additional demands are placed on the configuration or form of the holes or perforations, as disclosed in the German Published Pat. No. 2,919,316, the manufacturer of such perforated drums is confronted with special problems.